C2 Manual Issue 18

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An ISO 9001 Company

INSTRUCTION MANUALC2

ISSUE 18

NOVEMBER 2008

Subsonic Wind Tunnel


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IMPORTANT SAFETY INFORMATION

All practical work areas and laboratories should be covered by local safety

regulations which must be fo

llowed at all times.

It is the responsibility of the owner to ensure that all users are made aware of

relevant local regulations, and that the apparatus is operated in accordance with those

regulations. If requested then Armfield can supply a typical set of standard laboratory

safety rules, but these are guidelines only and should be modified as required.

Supervision of users should be provided whenever appropriate.

Your C2 Subsonic Wind Tunnel has been designed to be safe in use when installed,

operated and maintained in accordance with the instructions in this manual. As with

any piece of sophisticated equipment, dangers may exist if the equipment is misused,

mishandled or badly maintained.

Electrical Safety

The equipment described in this Instruction Manual operates from a mains voltage

electrical supply. It must be connected to a supply of the same frequency and voltage

as marked on the equipment or the mains lead. If in doubt, consult a qualified

electrician or contact Armfield.

The equipment must not be operated with any of the panels removed.

To give increased operator protection, Armfield recommends that a Residual Current

Device (RCD), alternatively called an Earth Leakage Circuit Breaker, be fitted to the

electrical supply for the equipment. Armfield supplies a suitable RCD, which may befitted if the laboratory supply does not already include such a device. If through

misuse or accident the equipment becomes electrically dangerous, the RCD will

switch off the electrical supply and reduce the severity of any electric shock received

by an operator to a level which, under normal circumstances, will not cause injury to

that person.

At least once each month, check that the RCD is operating correctly by pressing the

TEST button. The circuit breaker MUST trip when the button is pressed. Failure to

trip means that the operator is not protected and the equipment must be checked and

repaired by a competent electrician before it is used.

NOTE:

This apparatus is classified as Education and Training Equipment under the

Electromagnetic Compatibility (Amendment) Regulations 1994. Use of the

apparatus outside the classroom, laboratory or similar such place invalidates

conformity with the protection requirements of the Electromagnetic Compatibility

Directive (89/336/EEC) and could lead to prosecution.


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Risk of Fire or Explosion

Use of this equipment may involve the presence of highly flammable and potentially

explosive liquid (Paraffin/kerosene, used in the air speed manometer). Details of the

substances intended for use with this equipment are given in the Operational

Procedures section.

It is the users responsibility to handle chemicals safely Keep flames, sparks and high-temperature surfaces well away from the

equipment

Ensure all electrical supplies and equipment are properly maintained andused to avoid the risk of electrical sparks

Prepare chemicals and operate the equipment in well ventilated areas Position the manometer out of direct sunlight and away from heat sources Only use chemicals specified in the equipment manual and in the

concentrations recommended

Follow local regulations regarding chemical storage and disposal Ensure that all users are made aware of the correct procedure in the event of

fire or explosion

Moving or Rotating Components and Fast Moving Air Streams

This apparatus has moving or rotating components.

Do not remove any protective guards while the equipment is in operation. When operating the apparatus ensure that long hair is tied back out of the

way, and that clothing and jewellery cannot come into contact with any

moving parts. Dangling items such as necklaces and neckties must be

removed or secured, and long hair must be secured, so that they cannot be

sucked into the wind tunnel inlet.

Do not touch any moving components while the apparatus is in use, or insertany item into any moving or rotating section of the equipment.

Ensure that the apparatus is switched off and that all moving parts have cometo rest before handling the equipment, except as described in the Operational

Procedures section of this manual.

Be aware that air will be moving quickly at the inlet and outlet of the windtunnel. There is a risk that light objects may be blown over or sucked into the

inlet.

To avoid possible damage to eyesight, avoid looking directly into the outletwhen the wind tunnel is in operation.


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Noise

This equipment generates noise when running.

Depending on operator comfort and local noise regulations, ear defendersmay be required.

Ensure that all local noise regulations are followed when positioning theapparatus for use.

Heavy Equipment

This apparatus is heavy.

The apparatus should be placed in a location that is sufficiently strong tosupport its weight, as described in the Installation section of the manual.

Use lifting tackle, where possible, to install the equipment. Where manuallifting is necessary then two or more people will be required for safety. All

should be made aware of safe lifting techniques to avoid strained backs,

crushed toes, and similar injuries.

Safety shoes and/or gloves should be worn when appropriate.


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SUBSONIC WIND TUNNEL

C2

Contents

1 Introduction to the Equipment ............ ............. .............. ............ .............. ............. ............ .............. ............. ....1

1.1 Diagram 1: The C2 Subsonic Wind Tunnel showing working section ............ ............ .............. ............. ....2

1.2 Diagram 2: Models available for use with C2 Subsonic Wind Tunnel ................... .............. ............. ........ 3

2 Description..........................................................................................................................................................4

2.1 Overview.....................................................................................................................................................4

2.2 C2-10 Tunnel..............................................................................................................................................4

2.3 Fan and Motor ...........................................................................................................................................4

2.4 Tunnel Inlet ................................................................................................................................................5

2.5 Air Speed Manometer.. .............. ............. ............ .............. .............. ............. ............ .............. ............. ........ 5

2.6 Fan Speed Controller.................................................................................................................................6

2.7 Wind Tunnel Balance .................................................................................................................................6

2.8 C2-13 Multi-Tube Manometer....................................................................................................................7

2.9 C2-14 Pressure Wing and Rake .................................................................................................................7

2.10 C2-15 Slot and Flap Aerofoil ............ ............. .............. ............ .............. ............. .............. ............ ............. 9

2.11 C2-16 Pitot Static Tube ............. ............. ............. ............. .............. ............. ............ .............. ............. ........ 9

2.12 C2-17 Yaw Probe .......................................................................................................................................9

2.13 C2-18 Drag Models....................................................................................................................................9

2.14 C2-19 Pressure Cylinder............................................................................................................................9

2.15 C2-20 Flutter Wing ....................................................................................................................................9

3 Operation..........................................................................................................................................................11

3.1 Use of the Wind Tunnel Balance .............. ............. ............ .............. ............. .............. ............. ............. .... 11

3.2 Tunnel Calibration...................................................................................................................................12

3.3 Controlling and Measuring Air Speed .....................................................................................................133.4 Using the C2-13 Multi-Tube Manometer ............ ............. .............. ............. ............ .............. ............. ...... 14

3.5 Using the C2-14 Pressure Wing and Rake ............ ............ .............. ............. .............. ............. ............. ....15

3.6 Using the C2-15 Slot and Flap Aerofoil...................................................................................................16

3.7 Using the C2-16 Pitot Static Tube............................................................................................................16

3.8 Using the C2-17 Yaw Probe.....................................................................................................................17

3.9 Using the C2-18 Drag Models .................................................................................................................17


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3.10 Using the C2-19 Pressure Cylinder ............ .............. ............. ............ .............. ............. .............. ............. 17

3.11 Using the C2-20 Flutter Wing............. .............. ............ ............. .............. ............. ............ .............. ......... 18

3.12 Using the H14-2 Computer Compatible Manometer Bank ............ .............. ............. .............. ............ ..... 18

4 Specifications......... .............. ............. ............ .............. ............. .............. ............ .............. ............. .............. ...... 19

4.1 Overall Dimensions..... ............. ............ .............. ............. .............. ............ .............. ............. .............. ...... 194.2 Electrical Supply ........... .............. ............ .............. ............. ............ .............. ............. .............. ............ ..... 19

4.3 Motor Rating ............ .............. ............. .............. ............ ............. .............. ............. ............ .............. ......... 19

4.4 Lift and Drag Balance........ ............. ............ .............. ............. ............ .............. ............. .............. ............. 20

5 Routine Maintenance................. ............. ............ .............. ............. ............ .............. ............. .............. ............. 21

5.1 General............. ............. .............. ............ .............. ............. ............ .............. ............. ............ .............. ..... 21

5.2 RCD test .............. ............ ............. .............. ............. ............ .............. .............. ............. ............ .............. .. 21

5.3 Fan Check ................................................................................................................................................21

5.4 Replenishing the Manometer Reservoir ............ ............ ............. .............. ............. ............ .............. ......... 21

5.5 Lubrication.... .............. ............. ............ .............. ............. .............. ............ .............. ............. .............. ...... 21

5.6 Spares.......................................................................................................................................................21

6 Theory...............................................................................................................................................................23

6.1 Index to Theory Section.......... ............. .............. ............ ............. .............. ............. ............ .............. ......... 23

6.2 Nomenclature .............. ............. ............ .............. ............. .............. ............ .............. ............. .............. ...... 24

6.3 Theory for C2-14 Pressure Wing and Rake .............. ............. ............ .............. ............. .............. ............. 25

6.4 Theory for C2-15 Slot and Flap Aerofoil .............. ............. ............ .............. ............. ............ .............. ..... 27

6.5 Theory for C2-16 Pitot Static Tube............ ............. ............. ............. .............. ............. ............ .............. .. 29

6.6 Theory for C2-17 Yaw Probe...................................................................................................................306.7 Theory for C2-19 Pressure Cylinder.............. ............. .............. ............ .............. ............. ............ ............ 31

6.8 Theory for C2-20 Flutter Wing ............ .............. ............. .............. ............ .............. ............. .............. ...... 32

7 Installation Guide ............................................................................................................................................37

7.1 Installing the C2-10 Subsonic Wind Tunnel....... ............. .............. ............ .............. ............. .............. ...... 37

7.2 Assembling the lift and drag balance.......... .............. ............. ............ .............. ............. .............. ............. 38

7.3 C2-13 Multi-Tube Manometer ............ .............. ............ ............. .............. ............. ............ .............. ......... 39

7.4 C2-14 Pressure Wing and Rake ...............................................................................................................39

7.5 2-15 Slot and Flap Aerofoil............. ............ .............. ............. ............ .............. ............. .............. ............. 40

7.6 C2-16 Pitot Static Tube and C2-17 Yaw Probe ............ ............. .............. ............. ............ .............. ......... 40

7.7 C2-18 Drag Models.............. ............ .............. ............. .............. ............ .............. ............. ............ ............ 40

7.8 C2-19 Pressure Cylinder........ ............. .............. ............ ............. .............. ............. ............ .............. ......... 41


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Introduction to the Equipment

The C2 Subsonic Wind Tunnel, with its accessories, provides a complete facility for the study of

subsonic aerodynamics.

The degree of accuracy of the tunnel and its associated instrumentation is more than adequate for

undergraduate education and research purposes. It has an adjustable, reversible air flow throughthe octagonal working section, and includes a direct reading air speed indicator and a two

component balance for lift and drag measurements.

The accessories available for use with the wind tunnel include a flat plate with probe, an aerofoil

cross-section wing (with rake) and a cylinder, both with pressure tapping points, for investigating

pressure variation over the aerofoil or cylinder cross-section, a slot and flap aerofoil for

investigations of control surfaces, a set of shapes for the investigation of drag, and a flutter wing.

Other available accessories are a Pitot static tube and a yaw probe.

C2-10 Subsonic Wind Tunnel and Accessories


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1.1 Diagram 1: The C2 Subsonic Wind Tunnel showing working section


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1.2 Diagram 2: Models available for use with C2 Subsonic Wind Tunnel


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Description

Where necessary, refer to the drawings on pages 2 to 3.

1.3 Overview

The C2 wind tunnel consists of a clear-sided working section with instrumentation for a

range of models, with a motor-driven fan mounted on the outlet side.

1.4 C2-10 Tunnel

The basic tunnel comprises a fibreglass contraction and diffuser section with a clear

acrylic (Perspex) parallel test section of 300mm octagonal section. The diffuser section is

bolted directly to a Formica table top; whereas the contraction (to which is attached the

test section) is clamped to two slider bars which, in turn, are bolted to the Formica table

top. The table top is supported on a square-section steel tube frame, mounted on fourcastors, two of which incorporate a lever-operated brake.

1.5 Fan and Motor

A five-bladed fan is driven by a heavy duty electric motor mounted at the outlet of the

diffuser section. The motor and fan are covered by a heavy gauge steel wire mesh guard.

The fan speed controller is fitted adjacent to the fan motor (see section 1.8).


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1.6 Tunnel Inlet

A honeycomb flow straightener is located within the entrance to the contraction cone.

1.7 Air Speed Manometer

The tunnel air speed is indicated on a sloping manometer, calibrated in metres/second,

connected to a manifold surrounding the upstream end of the test section. Four equally

spaced static orifices, connected to the manifold, minimise the possibility of interference

effects from a model mounted in the test section.


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1.10 C2-13 Multi-Tube Manometer

This option is a twenty-tube manometer, with the manometer tubes mounted on a board.

A reservoir, filled with manometer liquid, is mounted on a vertical rod at the left of the

board. The datum manometer tube levels may be adjusted to convenient heights before

commencing an experiment. A plastic tube connects the reservoir to the base of themanometer manifold assembly. Each tube is mounted in O-ring fittings top and bottom, to

allow replacement if necessary.

The angle of the board may be adjusted to several different positions and clamped in any

selected position. The scale length is 370mm.

When using the manometer system with the tunnel it is important to bear in mind that the

working section is under suction, i.e. all stagnation pressures are below atmospheric.

Thus, in general, it is necessary to connect one manometer tube to the wind speed static

pressure line to provide a datum for measurements in the tunnel. If another tube is left

open to atmosphere then absolute pressures in the tunnel may be determined by relating

the tunnel datum to measured barometric pressure.

1.11 C2-14 Pressure Wing and Rake

The C2-14 accessory is designed to replace the lift and drag balance during use.

The pressure wing is a two-dimensional wing profile, manufactured to NACA 0015,

aerofoil section, with eleven pressure tapping points around the centre chord, flush with

the wing surface. The wing is mounted in a vertical plane in the working section, and the

angle of attack is adjustable. The appropriate size cover plates should be used to block up

the free area of slot in the base of the tunnel.


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A simple technique allows visualisation of the airflow around the wing (this may also be

used with the cylinder and any of the other optional models available for use with C2-10).

A lightweight twine follows the flow contour around the model and shows if and where

boundary layer separation (breakaway) occurs and where the flow becomes turbulent or

reverses.

The twine passes through a stainless steel L shaped tube, mounted in a gland that islocated in the floor of the working section at the upstream end.

A simple adjustment arrangement allows the length and position of the twine to be varied.

The vertical position of the twine can be varied by sliding the L shaped tube up or down

in the gland. The horizontal position of the twine can be varied by rotating the L shaped

tube in the gland. The length of the twine can be varied by allowing more or less twine to

pass through the tube then securing the twine to the tube by sliding the O ring over the

end of the tube. Adjustment of the length is best carried out when the Wind Tunnel is

operating. The end of the twine should be tied to the O ring before operating the fan so

that the twine cannot accidentally enter the working section and become entangled with

the fan.

The C2-14 also includes a 25mm diameter solid cylinder.

A wake survey rake, consisting of an array of eighteen small diameter total head tubes, is

also supplied that may be mounted behind the aerofoil or the cylinder to measure the

variations in pressure downstream due to the wake behind the model.

The tappings on the aerofoil or wake survey rake should be connected to the C2-13 multi-

tube manometer or equivalent.


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1.12 C2-15 Slot and Flap Aerofoil

The C2-15 aerofoil is machined to NACA 0015 profile. It is equipped with an adjustable

leading edge slot and trailing edge flap, and is used with the lift and drag balance supplied

as part of the standard C2-10 wind tunnel. The angle of attack is adjustable, as are the

distance of the slot from the leading edge and the angle of the trailing edge flap.

1.13 C2-16 Pitot Static Tube

The C2-16 Pitot static tube is constructed using 4mm diameter stainless steel tube with a

collet type mounting chuck to facilitate full traverse across the working section. It is of

Prandtl design and may be used with a negligible correction up to angles of yaw of at least

5 degrees. The two tappings should be connected to the C2-13 multi-tube manometer or

equivalent.

1.14 C2-17 Yaw Probe

This accessory is constructed using 4mm diameter stainless steel tube with a collet typemounting chuck to facilitate full traverse across the working section. It is of the three-hole

type with centre hole for total pressure determination. The three tappings should be

connected to the C2-13 multi-tube manometer or equivalent.

1.15 C2-18 Drag Models

Five drag models are included with this accessory, all of the same equatorial diameter:-

Sphere

Hemisphere, convex to air flow direction

Hemisphere, concave to air flow directionCircular disc

Streamlined shape

In addition to the above models, a spare support rod is provided for drag calibration

purposes.

1.16 C2-19 Pressure Cylinder

The C2-19 is a polished cylinder of 50mm diameter, and replaces the lift and drag balance

in the wind tunnel during use. It has 19 equi-spaced tapping points around half of the

circumference, i.e. at 10 intervals between 0 and 180 inclusive. The tappings should beconnected to the C2-13 multi-tube manometer or equivalent.

1.17 C2-20 Flutter Wing

The Flutter Wing is constructed of solid balsa wood and is a two-dimensional

symmetrical aerofoil to NACA.0015 specification. The aerofoil has aluminium end plates


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and is supported at each corner by two springs. These eight suspension springs simulate

the flexural and torsional structural characteristics of a real three-dimensional wing.


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1.19 Tunnel Calibration

The tunnel is fitted with an inclined manometer which is calibrated in metres per second

to give a direct reading of air velocity in the working section. This indicator operates on

the Venturi principle, being connected to static orifices before and after the inlet

contraction in the wall of the tunnel.

NOTE: The inclined manometer can only be used to measure the air velocity in thenormal/forward direction. When the direction of the air flow is reversed, for special

applications, the flexible connections to the manometer must be disconnected to prevent

the manometer fluid from being ejected.

Before the tunnel is used for quantitative results it will be necessary to check the accuracy

of this indicator since no account is taken of velocity profile across the working section.

(The calibration may also be used as a student exercise).

Calibration requires the Pitot Static Tube (C2-16) to be used in conjunction with the

Manometer Board (C2-13). Both items should be installed in accordance with the

instructions given in the Installation Guide (page 37).

Application of Bernoulli's Equation to the Pitot Static Tube provides the relationship:-

v =2P

a

where

P is the difference in pressure between the total and static tappings

(N/m2).

a is the density of air (kg/m3).

v is the point velocity (m/s).

P is measured using the Tilting Manometer when P = mgh

where

m = manometer fluid density (kg/m3).

g = gravitational constant (9.81).

h = true difference in manometer heights.

Now

h = d sin

where

d = indicated difference in levels on the tilted

manometer.

= angle of inclination to the horizontal.

The reciprocal of sin which may be called k is marked on the manometer tilt scale as a

magnification factor (x1.5, x2 or x3)


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so that

h = d/k

and P = mgd/k

Method

1 Set up the Pitot static tube in the side wall of the working section with thenose horizontal and facing the air stream.

2 Adjust the tilting manometer to an angle of 30 (x2), clamp it, and connectthe total and static lines from the Pitot tube.

3 Zero the direct reading velocity indicator.4 Switch on the motor and adjust the fan speed to give a suitable deflection

on the direct reading velocity indicator.

5 Read off the difference in length of the total and static heads on theinclined manometer. Readings should be repeated as the Pitot tube is

traversed across the working section, ensuring that the nose is maintained

horizontal. The average difference should be established and the mean air

speed calculated.

6 Repeat for several values of air speed.7 Plot graph of calculated air speed using the Pitot static tube against the

direct reading air speed indicator.

NOTE:

When taking readings using the Pitot static tube, point velocities are being measured. By

traversing the working section, a velocity profile may be established. This profile may beused to determine the mean velocity in the section, taking into account the size of models,

positions of tappings, etc. i.e. In the case of a stationary model with fixed pressure

tappings at the centre, the reduced velocity at the walls should be ignored. However, in

the case of a lift/drag model, the mean velocity should include any deviation within the

length of the model.

1.20 Controlling and Measuring Air Speed

With power connected to the fan speed controller,

the display will flash showing the frequency

output when the fan was used previously, the redHz LED will flash and the green Panel Control

LED will illuminate to indicate that the controller

is ready for operation. The fan will not operate at

this point.

Set the required frequency output using the raise or lower keys then press the RUN key to

start the fan which will accelerate up to the set frequency. The Hz LED will then

illuminate and the display will show the running frequency. To change the frequency


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press the raise or lower key as required until the required frequency is indicated (or the

required air speed is indicated on the inclined manometer).

To stop the fan press the STOP key which will decelerate the fan until it is stationary.

When pressing the raise or lower keys the right hand digit will change first, followed by

each digit to the left if the key is remains depressed.

Note: If using a model which may be damaged or manometer fluid may be lost by

operating the tunnel at high speed then it is important to set the frequency to a low value

before pressing the RUN key.

The fan speed controller is configured for normal operation with the air flowing from the

bell mouth entry towards the working section. If for a special application it is required to

operate the tunnel with the direction of the air reversed then it will be necessary to

reposition a link inside the controller to allow the fan to operate in reverse. If this action

is necessary refer to the IMO Jaguar VXS Users Guide supplied with the equipment.

NOTE: When operating the tunnel with the air flow reversed it will be necessary

to disconnect the inclined manometer, by removing the flexible

connections, to prevent the manometer fluid from being ejected.The actual air velocity in the tunnel is indicated

on the sloping manometer directly in

engineering units of metres/second. The output

frequency of the fan speed controller can be

adjusted in steps of 0.01 Hz to give the required

air velocity.

1.21 Using the C2-13 Multi-Tube Manometer

The manometer board is used by connecting one or more flexible tubes from the pressure

tapping(s) of the model under test to the top of one or more of the manometer bank tubes.

Where multiple connections are made it is strongly suggested that the tubes be connected

to the manometer bank in the same sequence as they are positioned on the model. The

tubes are numbered to assist in this.

The angle of the board may be adjusted to several different positions, and clamped by

means of the knurled screws in any selected position, in order that magnification of the

readings may be obtained.

When using the manometer system with the tunnel it is important to bear in mind that the

working section is under suction, i.e. all stagnation pressures are below atmospheric.

Thus, in general, it is necessary to connect one manometer tube to the wind speed staticpressure line to provide a datum for measurements in the tunnel. If another tube is left

open to atmosphere then absolute pressures in the tunnel may be determined by relating

the tunnel datum to measured barometric pressure.


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1.22 Using the C2-14 Pressure Wing and Rake

For all experiments using the pressure wing or rake, the lift and drag balance should be

removed and stored on its separate stand.

Pressure wing

The pressure wing is mounted in a vertical plane in the working section. The angle of

attack is adjusted by means of screws inboard of the wing end support blocks.

Appropriate size cover plates should be used to block up the free area of slot in the base

of the tunnel after mounting the model and after making changes to the angle of attack.

The aerofoil model is instrumented with pressure tappings on one surface only, as the

aerofoil is of symmetrical cross-section. Pressure distributions on the upper and lower

surfaces may therefore be obtained by using +ve and -ve angles of attack respectively. To

obtain a complete set of results, matching values of +ve and ve angles should be chosen

for taking readings.

Record pressure distribution for the upper and lower surfaces of the aerofoil at different

angles of attack from = 0 up to and beyond stall. Manometer levels should be noted

relative to a tunnel static datum level. Results obtained may be plotted on lines normal tothe aerofoil surface to give pressure distribution curves for each angle of attack.

Experiments may be carried out at different air velocities and the pressure distribution

curves compared for a fixed angle of attack.

Flow Visualisation

A simple technique allows flow visualisation around the wing (this may also be used with

the cylinder and any of the other optional models available for use with C2-10). A

lightweight twine follows the flow contour around the model and shows if and where


reverses.

The twine passes through a stainless steel L shaped tube that is located by a gland in thefloor of the working section at the upstream end.



in the gland. For optimum visualisation it is suggested that the vertical position of the

twine is adjusted to coincide with mid height in the working section.

The horizontal position of the twine can be varied by rotating the L shaped tube in the

gland.

The length of the twine can be varied by allowing more or less twine to pass through the

tube then securing the twine to the tube by sliding the O ring over the end of the tube.

Adjustment of the length is best carried out when the Wind Tunnel is operating. The end

of the twine should be tied to the O ring before operating the fan so that the twine

cannot accidentally enter the working section and become entangled with the fan.

After use with C2-14, the L shaped tube can be left in position inside the wind tunnel

and used to indicate the flow patterns around other models.


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Cylinder

The cylinder is also mounted in a vertical plane direction, and clamped by means of the

large washers (one to be placed each side of the slot in the tunnel base) and knurled screw

in the end of the cylinder. The cylinder should be mounted at the most upstream end of

the slot. Appropriate size cover plates should be used to block up the free area in the base

of the tunnel, as for the pressure wing.Rake

Wake traverses of total head may be made for either the aerofoil or the cylinder, by

placing the rake approximately 100mm behind the model, with the total head tubes

pointing upstream. The rake has two slots in the base, to enable the unit to be positioned

appropriately, and clamped in the tunnel base slot. The numbered tubing should be taken

to the Multi Tube Manometer C2-13 or an equivalent.

1.23 Using the C2-15 Slot and Flap Aerofoil

The C2-15 Slot and Flap Aerofoil is mounted vertically in the lift and drag balance. The

angle of attack of the aerofoil may be varied by means of the protractor top of the balance,then locked in position using the locking device. The distance of the slot from the leading

edge may be adjusted by means of the two set screws at each end of the model, as can the

angle of the trailing edge flap.

The drag counterbalance weight should be adjusted to give null deflection on the

indicator with no air flow. As the aerofoil is symmetrical about the support point, no

adjustment to the lift counterbalance weight should be necessary. An appropriately sized

cover plate must be positioned over the slot in the base of the tunnel after the model has

been positioned. Failure to do this will result in poor characteristic curves caused by air

having a transverse velocity component.

Care should be exercised when determining the angle of incidence of the aerofoil to theair stream. A datum position (i.e. = 0) should be obtained where the lift component of

the symmetrical aerofoil, without addition of slot or flap, is zero. All readings should be

corrected to this datum. A set of performance curves for the aerofoil are included in the

theory section for the aerofoil (page 27). These show lift and drag characteristics for a

typical production aerofoil at varying angles of incidence to the air stream. The curves are

included for guidance only since results for a specific aerofoil will depend on inherent

manufacturing tolerances. It should be noted that the curves are plotted as lift and drag

coefficients against angle of incidence.

1.24 Using the C2-16 Pitot Static Tube

The Pitot static tube has pressure tappings positioned so as to provide a differential

pressure reading from the instrument. A tapping in the nose of the probe provides a total

head (stagnation pressure) reading. Tappings around the body of the probe provide a static

head reading. The velocity of the fluid may be calculated from the difference between the

two head readings, as described in the theory section (page 29).


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1.25 Using the C2-17 Yaw Probe

The C2-17 is designed to be used in conjunction with other models, where velocity and

pressure distributions are of interest. The probe should be inserted through the side of

walls of the test section as follows:

Remove the red plastic cover plug from the side of the tunnel.

Unscrew the collet

Slide the instrument through the hole

A coupling on the stem of the probe engages in the female thread of the wall

fitting and should be screwed up tight.

Traverses may be made by unscrewing the smaller coupling on the stem from the

larger and adjusting the position of the probe as required.

The Manometer Board, C2-13 is used to monitor the pressure readings. Connections

should be made to the manometer board from all three probe holes.

The probe should be calibrated before use by running the wind tunnel without models but

with the probe in place. The set screw in the aligning block should be loosened and theprobe turned in the block until the pressure readings from the outside two holes give

identical readings, indicating that the central hole is aligned with the undisturbed air flow.

The set screw is then tightened to hold the probe in the correctly calibrated position.

1.26 Using the C2-18 Drag Models

Mount the required C2-18 drag model in the lift and drag balance. Two pins are situated

at the base of the support rod of each model. These locate in the balance socket in such a

way that axis-symmetric flow will occur over the model with the height between model

centre line and balance knife edges correct for the balance calibration.

Each model is mounted in the balance in the same way. Adjustment of the dragcounterbalance weight will be necessary for each model to achieve null deflection with no

air flow. This is due to weight differences between the models.

In order to give accurate results for drag, it is necessary to take into account the drag of

the support spindle. To give a close approximation of this effect, a spare spindle is

provided, for which a separate drag velocity curve may be determined. The appropriate

drag of the spindle may then be deducted from the total drag measured for a particular

model and support at a given velocity.

Whilst taking results it is important to reduce the slot in the tunnel base as much as

possible, using the cover plates provided.

1.27 Using the C2-19 Pressure Cylinder

Remove the lift and drag balance before mounting the C2-19 pressure cylinder. The

pressure cylinder is mounted vertically, and clamped into position at the upstream end of

the slot in the tunnel base using the large knurled nut. The pressure tapping points (taken

through the tunnel base) should be connected to the C2-13 manometer board or

equivalent.


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In order to ensure that the first tapping hole is at 0 to the air stream, two marks have been

made on the tunnel base. These should be aligned with appropriate marks on the flange at

the lower end of the cylinder.

A suitable cover plate should be placed over the remaining slot area in the base of the

tunnel.

The air velocity should be adjusted to give a reasonable spread of manometer levels, withthe board inclined at 30 degrees to the horizontal (x2). Manometer levels for each tapping

point should be recorded relative to a datum static tapping in the tunnel wall. The cylinder

may be turned through 180 and the test repeated to demonstrate the symmetry of the

pressure profile.

The test may be repeated for differing air velocities and pressure distributions plotted for

0 to 180. A theoretical distribution may be plotted from the relationship

1.28 Using the C2-20 Flutter Wing

Before placing the model in the Wind Tunnel, ensure that the suspension springs are

located correctly in the leading hole at each corner and each has zero displacement at rest.Spurious results will be obtained if these points are not checked.

Ensure that the restraining cords at each corner effectively limit maximum displacement

within the range of the springs.

Position the model in the Wind Tunnel ensuring that incidence is set at a low angle, i.e.

less than 5.

Increase the air speed in small increments until flutter is just initiated. Check that this is

the lowest speed at which flutter can be sustained.

This is the critical flutter speed Uf.

The flutter frequency may be determined by means of a stroboscope (not supplied).

1.29 Using the H14-2 Computer Compatible Manometer Bank

The C2 and accessories may be used in conjunction with the Armfield H14-2 from the

Armfield Hydraulic Instruments range. However, the H14-2 only provides 16 channels

rather than the 20 manometer tubes available with the C2-13. Some tapping points must

therefore be left unconnected when using certain of the C2 accessories. To obtain

symmetrical results, the following connections are suggested:

C2-14 wake survey rake: Connect tubes 2-7 and 9-18

C2-19 pressure cylinder: Connect tubes 2 to 17

NOTE: As the H14-2 is primarily designed for use with water as the working fluid, the

scaling may be too large for good accuracy at low flow rates within the wind tunnel.


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Specifications

1.30 Overall Dimensions

Height: - 1.83 m

Length - 2.98 m

Width - 0.80 m

Working Section - 300mm octagonal x 450mm long

1.31 Electrical Supply

C2-10-A C2-10-B C2-10-G

Green/yellow lead Earth (Ground) Earth (Ground) Earth (Ground)

Brown lead Live (Hot) Live (Hot) Live (Hot)

Blue lead Neutral Neutral Neutral

Fuse rating 10A 20A 10A

Voltage 220-240V 110-120V 220V

Frequency 50Hz 60Hz 60Hz

The equipment requires connection to a single-phase fused electrical supply. The mains

cable supplied with the equipment is terminated with a plug to suit the local electrical

supply. Three versions of the C2-10 are available: -

C2-10-A 230V/1ph/50Hz mains lead fitted with a 2 pin Shuko European style

plug with adaptor to 3 pin UK style plug.

C2-10-B 120V/1ph/60Hz Equipment as C2-10-G below but supplied with a

separate transformer to step-up the local supply voltage from 120V to

230V. The lead on the transformer is fitted with a 3 pin NEMA 5-30P

plug.

The transformer should be sited adjacent to the 120V mains outlet socket

in the laboratory, in a dry location. The mains lead from the C2-10 is

simply plugged into the 230V outlet socket on the front of the transformer.

The transformer is protected by a circuit breaker, located at the rear, with a

reset button in the event of a fault.

If a 220-230V NEMA 6-15R outlet is available in the laboratory then the

lead on the C2-10 can be plugged directly into the outlet (transformer not

used).

C2-10-G 220V/1ph/60Hz mains lead fitted with 3 pin NEMA 6-15P plug.

1.32 Motor Rating

1.5 kW


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1.33 Lift and Drag Balance

Maximum Balance Rating Lift - 7.0N

Maximum Balance Rating Drag - 2.5N

Sensitivity of Balance - 0.01N

Range of lift measurement : 0 - 7.0 N (1.574 lb.f)

Range of drag measurement : 0 - 2.5 N (0.562 lb.f)

Sliding Weights Mass (g) Mass (lb.m)

Primary drag 411 0.906

Secondary drag 103 0.227

Primary lift 1124 2.48

Primary drag 187 0.412

Distance between model centre line and drag arm knife edges: 308.5mm (1.012 ft)


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Routine Maintenance

To preserve the life and efficient operation of the equipment it is important that the equipment is

properly maintained. Regular maintenance of the equipment is the responsibility of the end user

and must be performed by qualified personnel who understand the operation of the equipment.

1.34 General

The equipment should be disconnected from the electrical supply when not in use.

1.35 RCD test

Test the RCD by pressing the TEST button at least once a month. If the RCD button does

not trip when the Test button is pressed then the equipment must not be used and should

be checked by a competent electrician.

1.36 Fan Check

The fan must be checked at regular intervals to ensure it is securely mounted. The fan is

secured by tightening the retaining screw at the end of the motor shaft.

1.37 Replenishing the Manometer Reservoir

Paraffin (kerosene) is volatile and some will evaporate from the manometer bank during

normal use. The manometer reserve may be replenished from the bottle supplied with the

kit. The fluid supplied is a blend of pure paraffin and dye with a specific gravity of 0.784

at 18.3C (65F).

1.38 Lubrication

No lubrication of the motor bearings is required. A few drops of SAE 30 grade oil on the

slider bars is beneficial, providing that the slider bars are kept clean.

Remove the castors annually and re-pack with ALVANIA3 grease.

1.39 Spares

Applications for spares should be sent to Armfield Ltd, Bridge House, West Street,

RINGWOOD, Hampshire, BH24 1DY, England, stating the serial number shown on thename plate.


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Theory

1.40 Index to Theory Section

Nomenclature.............................................................................................................................................................24

Theory for C2-14 Pressure Wing and Rake............ ............. ............ .............. ............. .............. ............. ............. .... 25

Theory for C2-15 Slot and Flap Aerofoil.................................................................................................................27

Theory for C2-16 Pitot Static Tube .............. ............. .............. ............ .............. ............. ............ .............. ............. ..29

Theory for C2-17 Yaw Probe ............. .............. ............ ............. .............. ............. ............ .............. .............. ............ 30

Theory for C2-19 Pressure Cylinder ............ ............. .............. ............ .............. ............. ............ .............. ............. ..31

Theory for C2-20 Flutter Wing................................................................................................................................32


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1.41 Nomenclature

Name Symbol Units Definition

Tunnel velocity v m/s v =2P

a

Difference between static and

stagnation pressureP

P = mgh

= mgd/k

Manometer fluid density m kg/m

Gravitational constant g N/m g = 9.81 N/m

True difference in manometer

levelh

d sin

= d/k

Indicated difference in levels

on tilted manometerd m Measured

Manometer inclination angle Measured

Magnification factor k Reciprocal of sin (Marked)

Chord length c m Measured

Kinematic viscosity of air Referenced

Reynolds Number Re - Re =

vc

Lift force LSv

2

CLDrag force D Sv

2CD

Area of aerofoil S Length x Span

Air Temperature T K Measured if desired

Air density kg/m Referenced

Coefficient of lift CL -2L

Sv2

Coefficient of drag CD -2D

Sv2

Angle of attack (incidence) Angle between chord of wing

and mean air flow direction


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1.42 Theory for C2-14 Pressure Wing and Rake

When setting the aerofoil at a chosen angle of attack it should be noted that the indicator

is subject to manufacturing tolerances. The aerofoil model is instrumented with pressure

tappings on one surface only. Pressure distributions on the upper and lower surfaces are

obtained at + ve and - ve angles of attack.

Record pressure distribution for the upper and lower surfaces of the aerofoil at different

angles of attack from = 0 up to and beyond stall. Manometer levels should be noted

relative to a tunnel static datum level.

Results obtained may be plotted on lines normal to the aerofoil surface to give pressure

distribution curves for each angle of attack.

Experiments may be carried out at different air velocities and the pressure distribution

curves compared for a fixed angle of attack.

Reynold's number (Re) may be obtained from the relationship

Re =

vc

where

v is the tunnel velocity

c is the chord length

is the kinematic viscosity of the air

A simple technique allows flow visualisation around the wing (this may also be used with

the plain cylinder any of the other optional models available for use with C2-10). A

lightweight twine follows the flow contour around the model and shows if and where


reverses.

The twine passes through a stainless steel L shaped tube that is located by a gland in the

floor of the working section at the upstream end.



in the gland. The horizontal position of the twine can be varied by rotating the L shaped

tube in the gland. The length of the twine can be varied by allowing more or less twine to

pass through the tube then securing the twine to the tube by sliding the O ring over theend of the tube. Adjustment of the length is best carried out when the Wind Tunnel is

operating. The end of the twine should be tied to the O ring before operating the fan so

that the twine cannot accidentally enter the working section and become entangled with

the fan.

The solid cylinder is also mounted in a vertical plane and clamped by means of the large

washers (one to be placed each side of the slot in the tunnel base) and knurled screw in


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the end of the cylinder. The cylinder should be mounted at the most upstream end of the

slot.

Wake traverses of total head may be made for either the aerofoil or the cylinder, by

placing the rake approximately 100mm behind the model, with the total head tubes

pointing upstream. The rake has two slots in the base, to enable the unit to be positioned

appropriately, and clamped in the tunnel base slot. The numbered tubing should be takento the Multi Tube Manometer C2-13.

It is important to place the appropriately sized cover plates over the remaining slot area in

the base of the tunnel.


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1.43 Theory for C2-15 Slot and Flap Aerofoil

Care should be exercised when determining the angle of incidence of the aerofoil to the

air stream. A datum position (i.e. = 0) should be obtained where the lift component of

the symmetrical aerofoil, without addition of slot or flap, is zero. All readings should be

corrected to this datum. A set of performance curves for the aerofoil are included

overleaf. These show lift and drag characteristics for a typical production aerofoil atvarying angles of incidence to the air stream. The curves are included for guidance only

since results for a specific aerofoil will depend on inherent manufacturing tolerances. It

should be noted that the curves are plotted as lift and drag coefficients against angle of

incidence.

These parameters are obtained from the standard equations:

L = Sv2CL and D = Sv

2CD

where

L = lift force

D = drag force

S = area of aerofoil (length x span)

v = air velocity

= air density

CL = lift coefficient

CD = drag coefficient

Then Lift coefficient CL =2L

Sv2

and Drag coefficient CD =2D

Sv2

In addition to the curves shown overleaf, the ratio of CL/CD may be plotted against angle

of incidence to demonstrate the efficiency of the aerofoil.


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Typical Lift and Drag Curves for the C2-15 Aerofoil

1 Aerofoil with split flap2 Aerofoil with leading edge slot3 Aerofoil alone


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1.44 Theory for C2-16 Pitot Static Tube

Application of Bernoulli's Equation to the Pitot Static Tube provides the relationship

(assuming the flow to be incompressible at the low velocities experienced within the

wind tunnel):-

v =

2P

a

where

P is the difference in pressure between the total and static

tappings (N/m2).

a is the density of air (kg/m3).

v is the point velocity (m/s).

P is measured using the Tilting Manometer when

P = mgh

where

m = manometer fluid density (kg/m3).

g = gravitational constant (9.81).

h = true difference in manometer heights.

Now

h = d sin

where

d = indicated difference in levels on the tilted

manometer.

= angle of inclination to the horizontal.

The reciprocal of sin which may be called k is marked on the manometer tilt scale as a

magnification factor (x1.5, x2 or x3)

so that

h = d/k

and P = mgd/k


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1.45 Theory for C2-17 Yaw Probe

The Yaw probe consists of a three Total head tubes; one central tube with two tubes located at

equal angles, on either side. This arrangement allows the direction of the air flow to be

determined and the central Total head tube to be accurately aligned with the direction of flow.

The three tappings on C2-17 should be connected to the C2-13 Inclined manometer or similar

device.

The Yaw probe should be rotated until the readings from the two side tappings are the same. At

this position the central Total head tube is pointing directly into the airstream and the magnitude

and direction can be measured.

Since the Yaw probe only incorporates a Total head tapping and no static tapping (as in the case

of the Pitot static tube C2-16) it will be necessary to relate the total head measurement from thecentral tapping to the static pressure inside the duct to determine the air velocity.


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1.46 Theory for C2-19 Pressure Cylinder

The air velocity should be adjusted to give a reasonable spread of manometer levels, with

the board inclined at 30 degrees to the horizontal (x2). Manometer levels for each tapping

point should be recorded relative to a datum static tapping in the tunnel wall. The cylinder

may be turned through 180 and the test repeated to demonstrate the symmetry of thepressure profile.

The test may be repeated for differing air velocities and pressure distributions plotted for

0 to 180. A theoretical distribution may be plotted from the relationship

P- Po

1

2v2

= 1 - 4 sin2

Where

P = measured pressure

po = static pressure

= air density

v = air velocity

= angle between the radius to the tapping point

and the tunnel axis

This gives the distribution for a cylinder in an ideal fluid and comparison with the

practical results obtained will reveal a significant difference on the downstream side of

the cylinder. This is due to the properties of a real fluid giving rise to breakaway and eddy

formation.


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1.47 Theory for C2-20 Flutter Wing

The analysis and control of the phenomenon of the flutter of an aerofoil in an air stream

has importance not only in the design of aircraft, but also civil and mechanical structures

such as bridges and towers.

Flutter is caused by damping between the aerodynamic forces generated by an aerofoil

and its inertial and structural stiffness, resulting in a binary instability between theflexural and torsional natural modes of vibration. The general equation of motion of an

aerofoil in an air stream is expressed in matrix form by:-

(Inertia) (Aero Damping)

-2

m, m xb( )m xB( ), I

+ i VSc1

z. ,1

.

mz. , m

.

+

(Aero Stiffness) (Structural Stiffness)

V2Sc

1z , 1

mz ,m

+

kt , 0

0, kr

z

=

0

0

Where

= frequency

= density of air

V = air speed

S = wing spanc = chord

m = moment

l = lift

kt = translational spring rate

kr = rotational spring rate

xb = distance c.g to centre rotation

At the critical flutter speed the solution of the equation is of the form:-Z = Ze

iwt

= eiwt

The aerodynamic derivatives

1,1z etc. are dependent upon the frequency, , so that

precise solution must be achieved using an iterative process for .


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Two-Dimensional Analysis of the Flutter Wing

The theoretical analysis of the two-dimensional model after Bisplinghoff requires that the

following physical parameters are determined:

1. The Centre of Rotation, cr2. The Centre of Gravity, cg3. The Translational Spring Constant, kt4. The Rotational Spring Constant, kr5. Aerofoil Chord, c6. Aerofoil Span, S7. The Mass of the Aerofoil, M8. The Moment of Inertia of the Aerofoil, IgThese parameters may be determined using the following procedures:

1. Centre of RotationSince the suspension springs are of equal stiffness, it may be assumed that this lies on

the transverse line of symmetry of the springs.

2. Centre of GravityThis may be determined simply for the section by balancing the Aerofoil over a knife

edge.

3. Translation Spring ConstantThis may be determined by measuring the static deflection of the spring due to a

known load.

4. Rotational Spring ConstantThis may be obtained by suspending the aerofoil on its springs, placing a known

concentrated load at a known distance from the centre of rotation, and measuring the

deflection at the leading and trailing edges of the aerofoil.

5. and 6. The Chord

Span and mass of the aerofoil are obtained by direct measurements.

7. Moment of InertiaThis may be calculated from the natural period of oscillation, determined by means of

a simple torsional pendulum.


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Calculation

The physical parameters given below were measured on the Armfield Flutter

Wing and should approximate to those of all Armfield Model Flutter Wings:

Constants: Specific mass of air = 1.23kg/m3

Gravitational constant g = 9.81m/sec2

The Flutter Speed = Ufm/sec:

Chord, c = 100mm,

b = 50mm,

Span, S = 230mm

s = 63.34mm,

s1 = 9.06mm :-

Therefore:-

Centre of Rotation, 1r = 40.9mm

Centre of Gravity, 1g = 43.9mm

Weight of Wing and End Plates, W = 59.5 x 10-3

kg

Ig = 0.41 x 10-4

kg.m2

Translational Spring Constant, kt = 558 N/m

Rotational Spring Constant, kr = 0.558 N.m/rad


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35

Hence natural structural frequencies:-

Translational, h =kt

W= 96.6 rad/sec

Rotational, =kr

Ig

= 116.0 rad/sec

Mass per Unit Span, M = W/S = 0.259 kg/m

The parameters are non-dimensional in the following manner:

=Distance from c.r. to mid - chord

semi - chord, bC m( )= 0.182

X =Distance from c.r. to c.g.

Semi - chord, b= 0.060

I =Ig

S= 1.78 104 kg.m 2/ m, inertia per unit span

Therefore

r2

=

I

M.b

2= 0.275

M

b2 = 26.8

h

= 0.834

Bisplinghoff's

analysis is for a simplified system with two degrees of freedom and curves

of Uf/b versus h/ are presented, bounded by the parameters:

M

b

2 ; X ;r2

The values of these parameters, calculated from the Armfield model, are compared with

the closest values given in the reference:-

Reference: Bisplinghoff R.L., Ashley H., Halfman, R.L., Aerolasticity,

Addison-Wesley Publishing Co. Inc. 1955


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r2

X M/b

2

Calculated from Armfield model 0.275 0.060 26.8

Reference* value 0.25 0.01 30.0

Thus interpolating from the reference curves:

U f

b. 1.75 Where b. = 5.8m/sec

Therefore calculated flutter speed, Uf= 10.2m/sec


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Installation Guide

1.48 Installing the C2-10 Subsonic Wind Tunnel

The apparatus should be carefully unpacked and the components checked against theAdvice Note (A copy of the Advice Note is supplied with this instruction manual for

reference).

Any omissions or breakages should be notified to Armfield Ltd within three days ofreceipt.

Any omissions or breakages should be notified immediately to the Insurance Agent statedon the Insurance Certificate if the goods were insured by Armfield Ltd. Your own

insurers should be notified immediately if insurance was arranged by yourselves.

Position the wind tunnel in position, ensuring that the position chosen is strong enough tosupport the weight of the apparatus. The frame is mounted on castors to assist in moving

the apparatus. For safety reasons it is preferable to position the inlet and outlet ends of the

tunnel such that it is not necessary to walk past them when the apparatus is in use (i.e.

avoid positioning the inlet or outlet facing a thoroughfare).

Remove the protective tape is placed from the end of the contraction and diffuser section(contraction end).

The wind tunnel balance (used for measuring lift and drag forces) is supplied partiallydismantled for safe packing. Match the supplied components against the packing list and

identify the following:

o Lift arm, together with the larger cylindrical counterbalance weight, largest slidingrectangular weight, protractor and cursor, model support rod and spindle block.

o Spindle, to which is attached the stabilising weight and cruciform damper vane.o Drag arm, together with the smaller cylindrical counterbalance weight, the smaller

of the two large sliding rectangular weights and the trunnion block.

o Two smaller sliding weights. The larger of these is the secondary lift weight, thesmaller the secondary drag weight.

o One litre of heavy gear oil.o Balance storage stand.

Before operating the equipment, it must be unpacked, assembled and

installed as described in this Installation Guide. Safe use of theequipment depends on following the correct installation procedure.


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1.49 Assembling the lift and drag balance

Push the stabilising weight spindle into the spindleblock.

Ensure that the cruciform vane arms are at 45 tothe balance arm, and then lock the spindle into

position with the grub screw mounted in the spindle

block (using the key provided).

Unlock the clamping screw and slide back wind tunnel working section to its fully openposition.

Remove oil level plug from damping pot and place any convenient empty container underthe oil reservoir plug hole.

Fill the damping pot with the supply of heavy gear oil, leaving the plug off for the timebeing.

Place the drag arm assembly on the support ring,such that the knife edges fit into the machined

grooves in the support.

The end of the drag arm should be within the cut-out ofthe null indicator.


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Place the lift assembly on the trunnionblock such that the knife edges fit into the

machined grooves in the trunnion block.

As the assembly is lowered, the damper vanes will displace some oil from the dampingpot through the plug hole. When the oil stops flowing, replace the plug.

Place the secondary sliding weights on their respective balance arms, i.e. the smaller onthe drag arm, the larger on the lift arm.

Slide all weights into their zero position and check that both balance indicators point tozero. If not, slacken the locking screws on the counterbalance weights with the key

provided, and adjust until zero is obtained. Re-tighten the screws.

The balance is now ready for use, although additional adjustment of the weights may berequired depending on the model used:o For any model that has its centre of gravity and lift coincident with vertical

spindle axis (including all Armfield accessories involving lift measurements), no

adjustment is required.

o For models where this is not the case, e.g. the Armfield Drag Models C2-18, it isnecessary to adjust the drag arm counter-weight until zero balance is obtained

with the model in position but with no air flowing through the tunnel.

When the balance is not required for model tests, the trunnion block and two balanceweights may be removed from the support ring, and the whole assembly placed in the

balance stand supplied separately.

1.50 C2-13 Multi-Tube Manometer

The Manometer Board is installed by bolting the two mounting brackets at the back of theboard through the hole provided on the table top, just to the right of the air speed

indicator.

The reservoir, to be filled with the manometer liquid, is mounted on a vertical rod at theleft of the board, such that the position of the datum manometer tube levels may be

adjusted to convenient heights before commencing an experiment. A plastic tube

connects the reservoir to the base of the manometer manifold assembly.

1.51 C2-14 Pressure Wing and Rake

The lift and drag balance should be removed and stored on its separate stand. The wing is mounted in a vertical plane in the working section, and secured in position by

two screws through the ceiling of the tunnel, and the thumb screw clamp through the slot

in the base.


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The tubing from the tapping holes is taken to the manometer board. Appropriate size cover plates should be used to block up the free area of slot in the base

of the tunnel.

The flow visualisation arrangement should be installed as follows:-Screw the gland into the tapping in the floor of the working section at the upstream end

(from the outside of the tunnel).

Feed the twine through the L shaped tube leaving a short length protruding from the

long leg of the tube.

Open the working section and insert the long leg of the L shaped tube through the gland

(after feeding the twine through the hole in the gland).

Tighten the gland sufficiently to retain the L shaped tube in position but to allow it to be

moved / rotated when required.

Outside the working section, tie the exposed end of the twine to the O ring then slide the

O ring over the end of the tube to retain the twine.

1.52 2-15 Slot and Flap Aerofoil

Fit the lift and drag balance as described previously, if not already fitted. Mount the aerofoil vertically in the lift and drag balance, and lock at the chosen angle of

attack.

Adjust the drag counterbalance to give null deflection on the indicator with no air flow.

1.53 C2-16 Pitot Static Tube and C2-17 Yaw Probe Remove the red plastic cover plug from the hole in the side of the test section. Slide the instrument through the hole. A coupling on the stem of the probe engages in the female thread of the wall fitting and

should be screwed up tight.

Connect the pressure tappings to the Manometer Board, C2-13. Position an appropriately sized cover plate is positioned over the slot in the base of the

tunnel.

Traverses may be made by unscrewing the smaller coupling on the stem from the largerand adjusting the position of the probe as required.

1.54 C2-18 Drag Models

Fit the lift and drag balance as described previously, if not already fitted. Position the spare spindle in the lift and drag balance so that the two locating pins at the

base of the support rod fit into the balance socket.


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Cover the remaining exposed slot in the tunnel base as much as possible using the coverplates provided.

Adjust the drag counterbalance weight to give null deflection with no air flow. Use the spindle to determine the drag of the support spindles of the drag models. The

spindle drag may then be subtracted from the total drag measured for each model. Once a

drag velocity curve has been established this may be kept with the wind tunnel and usedfor future calculations.

Each model is mounted in the balance in the same way as the spare spindle. The locatingpins ensure that axis-symmetric flow will occur over the model with the height between

model centre line and balance knife edges correct for the balance calibration.

The remaining slot area must be covered with the plates provided. Adjustment of the drag counterbalance weight will be necessary for each model to

achieve null deflection with no air flow. This is due to weight differences between the

models.

1.55 C2-19 Pressure Cylinder

The lift and drag balance should be removed and stored on its separate stand. Mount the C2-19 vertically in the slot in the tunnel base. In order to ensure that the first

tapping hole is at 0 to the air stream, two marks have been made on the tunnel base.

These should be aligned with appropriate marks on the flange at the lower end of the

cylinder.

Clamp the cylinder into position at the upstream end using the large knurled nut. Take the pressure tapping tubes through the tunnel base, and connect them to the

manometer board.

Cover the remaining slot area in the base of the tunnel with a suitable cover plate.

Refer to the Operational Procedures section in the product manual for

further information.


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Main Office: Armfield Limited

Bridge House

West Street

Ringwood

Hampshire

England BH24 1DY

Tel:

Fax:

Email:

Web:

+44 (0)1425 478781

+44 (0)1425 470916

[email protected]

http://www.armfield.co.uk

US Office: Armfield Inc.

436 West Commodore Blvd (#2)

Jackson, NJ 08527

Tel:

Fax:

Email:

(732) 928 3332

(732) 928 3542

[email protected]

Date post:	03-Apr-2018
Category:	Documents
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C2 Manual Issue 18

Documents